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10) 9001 



Bureau of Mines Information Circular/1985 



Laboratory Wear Testing Capabilities 
of the Bureau of Mines 

By R. Blickensderfer, J. H. Tylczak, and B. W. Madsen 




UNITED STATES DEPARTMENT OF THE INTERIOR 



.751 

AflNES 75TH A^^ 



J nVorrnati on circu-ic^r {^Unittd ouxres, (e>arca.fcc OT I I'ne^y 



information Circular 9001 

Laboratory Wear Testing Capabilities 
of the Bureau of Mines 

By R. Blickensderfer, J. H. Tylczak, and B. W. Madsen 



UNITED STATES DEPARTMENT OF THE INTERIOR 
William P. Clark, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 





UNIT OF MEASURE 


ABBREVIATIONS USED 


IN THIS REPORT 


°c 


degree Celsius 


L/min 


liter per minute 


cm 


centimeter 


m 


"'" ^t\l^^ 


cm^ 


square centimeter 


mg 


milligram 1 ' 


c/min 


cycle per minute 


mln 


minute / ^' ^,1 
millimeter -h, ' 


deg 


degree 


mm 


g 


gram 


mm' 


cubic millimeter 


g/mln 


gram per minute 


m/mln 


meter per minute 


HB 


Brinell hardness 


mm'/m 


cubic millimeter per meter 


h 


hour 


vm 


micrometer 


HRC 


Rockwell C hardness 


m/s 


meter per second 


in 


inch 


N 


newt on 


J 


joule 


pet 


percent 


kg 


kilogram 


psl 


pound per square inch 


kPa 


kilopascal 


rpm 


revolution per minute 


kW 


kilowatt 


s 


second 


L 


liter 


wt pet 


weight percent 



Library of Congress Cataloging in Publication Data: 




Blickensderfer, Robert 

Laboratory wear testing capabilities of the Bureau of Mines. 

(Information circular ; 9001) 

Bibliography: p. 34-36. 

Supt. of Docs, no.: I 28.27:9001. 

1. Mechanical wear— Testing. I. Tylczak, J. H. (Joseph H.). II. 
Madsen, B. W. (Brent W.). III. Title. IV. Series: Information circu- 
lar (United States. Bureau of Mines) ; 9001. 



TN295.U4 [TA418.4] 622s [622'.028] 84-600209 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Description of tests and equipment 2 

Abrasive wear 3 

Dry-sand, rubber-wheel abrasive wear test 3 

DSRW equipment and specimen. 4 

DSRW procedure 4 

DSRW results and discussion 5 

Taber Abraser test 5 

Taber Abraser equipment and specimens 5 

Taber Abraser procedure 6 

Abrasion resistance test of refractory materials 7 

Dry-particle erosive wear test 7 

Dry-particle equipment and specimen 7 

Dry-particle procedure. 9 

Dry-particle typical results 9 

Elevated-temperature, dry-particle erosive wear test 10 

Elevated-temperature erosive equipment and specimens 11 

Elevated-temperature erosive procedure 11 

Elevated-temperature erosive results 11 

Low-angle slurry pot test 12 

Slurry pot equipment and specimens 13 

Slurry pot procedure 16 

Slurry pot results 16 

Jaw crusher gouging abrasion test 17 

Jaw crusher equipment and specimen 17 

Jaw crusher procedure 18 

Jaw crusher typical results 18 

Ball mill wear test 20 

Ball mill equipment and specimens 20 

Ball mill procedure 21 

Ball mill results and discussion 21 

Pin-on-drum abrasive wear test 22 

Pln-on-drum equipment and specimen 22 

Fln-on-drum procedure 23 

Pin-on-drum results and discussion 24 

High-speed impact-gouging test 25 

High-speed Impact equipment and specimen 25 

High-speed impact procedure 26 

Impact-spalling wear 26 

Ball-on-block Impact-spalling test 27 

Ball-on-block equipment and specimen 27 

Ball-on-block procedure 30 

Ball-on-block results and discussion 30 

Ball-on-ball impact-spalling test 31 

Ball-on-ball equipment and specimens 31 

Ball-on-ball procedure 32 

Ball-on-ball results and discussion 32 

Summary 32 

References 34 



ii 



ILLUSTBIATIONS 

Page 

1 . Dry-sand, rubber-wheel abrasive wear test machine 4 

2. Taber Abraser test, schematic 6 

3 . Wear pattern produced by the Taber Abraser 6 

4. Abrasion resistance test of refractory materials, schematic 8 

5. Dry-particle erosive wear test apparatus , schematic 9 

6. Dry-particle erosive wear test, specimen chamber 10 

7. Elevated— temperature erosion tester, schematic 12 

8. Low-angle slurry pot equipment, schematic 14 

9 . Low-angle slurry pot test equipment 15 

10. Jaw crusher gouging wear test machine, schematic 18 

11. Jaw crusher gouging wear test machine..... 19 

12. Small ball mill with specimens, liquid, and rock 21 

13. Ball mill test equipment, schematic 21 

14. Pin-on-drum abrasive wear test machine, schematic 23 

15. Pin-on-drum abrasive wear test machine 24 

1 6. High-speed impact-gouging test machine , schematic 26 

17. High-speed impact-gouging test machine 27 

18 . Ball-on-block impact-spalling test machine , schematic 28 

19. Ball-on-block impact-spalling test machine 29 

20. Ball-on-ball impact-spalling test machine, schematic... 31 

TABLES 

1. Standard conditions for the dry-sand, rubber-wheel abrasion test 4 

2 . Typical dry-sand , rubber-wheel abrasive wear data. 5 

3. Typical dry-particle erosive wear data 9 

4 . Hot erosive wear of several materials 11 

5. Typical low-angle slurry wear data for several metallic specimens 16 

6. Typical Jaw crusher gouging wear data 20 

7. Ball mill erosion-corrosion of several materials 22 

8 . Typical pin-on-drum wear test data 24 

9 . Typical ball-on-block impact-spalling data 30 

10. Summary of Bureau of Mines wear tests 33 

1 1 . Summary of wear tes t parameters 33 



LABORATORY WEAR TESTING CAPABILITIES OF THE BUREAU OF MINES 

By R. Blickensderfer, ^ J. H. Tylczak, ^ and B. W. Madsen ^ 



ABSTRACT 

The laboratory wear testing capabilities of the Bureau of Mines are 
described. Wear tests are used to support the Bureau's research ef- 
forts toward reducing the wear of equipment used for mining and miner- 
als processing and any wear involving a loss of strategic or critical 
materials. The emphasis is on abrasive wear because it accounts for 
most of the wear losses that occur in mining and minerals processing 
equipment. Spalling wear, caused by repetitive impact in grinding 
equipment, also is included. Ten abrasive wear tests, including high- 
stress and low-stress and two-body and three-body conditions, are 
described: dry-sand, rubber-wheel abrasive wear; Taber Abraser; abra- 
sion resistance of refractory materials; dry-particle erosive wear; 
elevated-temperature, dry-particle erosive wear; low-angle slurry 
pot; jaw crusher gouging wear; ball mill wear; pin-on-drum abrasive 
wear; and high-speed impact gouging. Two repetitive impact tests are 
described: ball-on-block impact-spalling and ball-on-ball impact- 
spalling. Test equipment, procedures, and specimens are described, and 
typical test results are presented and discussed. 



^Metallurgist, Albany Research Center, Bureau of Mines, Albany, OR. 



INTRODUCTION 



Wear is a major problem in the mining 
industry and occurs on a wide variety 
of items, such as excavator teeth, rock 
drill bits, crushers, slushers, ball 
mills and rod mills , chutes , slurry 
pumps, and cyclones. Wear results in a 
significant cost to the mining industry 
in terms of direct replacement costs, 
downtime, and maintenance. The Bureau of 
Mines is conducting research on various 
types of wear processes and materials. 
Wear mechanisms and the effects of vari- 
ables such as alloy composition and heat 
treatment are being studied with the ul- 
timate aim of devising alloy systems that 
reduce wear and significantly reduce the 
loss of critical and strategic metals. 
In order to support this research, a var- 
iety of laboratory test equipment has 
been purchased or constructed. 

Although numerous types of wear tests 
have been reported, most are beset by 
lack of reproducibility or are too spe- 
cialized to be of general interest. Only 
eight wear test practices have been pub- 
lished by the American Society for Test- 
ing and Materials (ASTM) , although others 
are in process. The G.2 committee of 
ASTM, which is concerned with all types 
of wear, is devoting considerable effort 
toward developing wear test standard 
practices and procedures. The Bureau is 
working with the G.2 committee in this 
effort. The ASTM has published an evalu- 
ation of wear testing (Jl^)^ and, more re- 
cently, a volume describing a wide range 
of types of wear tests (_2 ) . Borik O) 
compared several abrasion tests on a var- 
iety of abrasion-resistant materials. 

An ideal laboratory wear test would 
be small in scale, produce highly repro- 
ducible data quickly, and simulate a 



wide range of field conditions. The test 
results should predict the wear of a 
material in actual service. Such a test 
is difficult to achieve because wear 
processes are dependent on a number of 
variables that are affected by time 
and scale. Some of these factors are 
frictional heating (lowering the flow 
stress), work hardening rate, size and 
nature of wear debris, nature of abrasive 
particles, microstructure of the materi- 
al, and environmental interactions. 

Consequently, hundreds of wear tests 
have been devised, each an attempt by an 
investigator to closely simulate a given 
wear situation while producing signifi- 
cant wear in a short time. There is a 
need to standardize and minimize the 
types of wear tests in order to make in- 
terlaboratory comparisons and to reduce 
the number of tests and types of test 
specimens required. At the same time, 
there is a need for the tests to more 
closely simulate a broader range of field 
conditions. 

It is hoped that the following descrip- 
tion of wear tests used by the Bureau 
will be helpful to other organizations 
involved in wear testing and wear re- 
search. The comparison of test parame- 
ters such as specimen size, duration of 
test, surface speed, etc. may be partic- 
ularly useful to those attempting to se- 
lect a suitable wear test. Also, this 
report may stimulate further ideas in 
wear testing and wear research that will 
eventually help reduce the tremendous 
losses in materials that result from 
equipment wear in mining and minerals 
processing in the United States as well 
as other countries. 



DESCRIPTION OF TESTS AND EQUIPMENT 



The Bureau of Mines has a total of 12 
types of wear test units in use. Ten of 

— ^ — 

''Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



these units are located at the Albany 
(OR) Research Center, where considerable 
research is being conducted on wear. The 
other two units are at the Rolla (MO) and 
Tuscaloosa (AL) Research Centers. Most 
of the Bureau's tests are related to 



abrasive wear, including erosive wear and 
slurry wear, because most wear problems 
in mining and minerals processing are 
caused by abrasive materials. Two tests 
involve impact-spalling wear — a major 
wear problem in crushing and grinding 
equipment. Other types of wear, such as 
adhesive wear and lubricated wear, are 
not being addressed. One study of wear 
between quartz and steel was conducted 
in 1976 at the Twin Cities (MN) Research 
Center (4^) , but the pin-wear test equip- 
ment that was used no longer exists. 
Similar pin-wear test equipment belonging 
to the University of Maryland was recent- 
ly used at the Avondale (MD) Research 
Center for evaluating molybdenum diboride 
coatings. 

Among the wear tests described, the 
dry-sand, rubber-wheel abrasion test is 
an ASTM standard practice (_5) and the 
abrasion resistance of refractory materi- 
als is an ASTM standard test method (6). 
Two of the tests, the jaw crusher gouging 
abrasion test and the dry-particle ero- 
sion standard practice, were recently 
published by the ASTM. Of the remaining 
eight tests, three are novel tests de- 
vised by the Bureau, namely, the ball-on- 
ball impact-spalling test, the high-speed 
impact-gouging wear test, and the low- 
angle slurry pot test. The other five 
types of tests described are not ASTM 
standards but have been reported by other 
laboratories. In several cases, the Bu- 
reau has modified or improved the earlier 
tests. 



are not pertinent to the thrust of the 
Bureau's research on wear of mining 
equipment . 

ABRASIVE WEAR 

Abrasive wear tests are frequently 
classified by the type of test equipment 
used; however, they can be classified in 
more general terms by the stress level 
and the geometrical arrangement of the 
components of the system (7^, pp. 8-9). 
If the load is sufficient to fracture the 
abrasive particles, the wear is called 
high-stress abrasive wear; if the parti- 
cles do not fracture significantly, it 
is called low-stress abrasive wear. The 
distinction between low-stress and high- 
stress conditions is not sharp. As for 
geometrical arrangement, if the abrasive 
particle is in contact with only one 
other object, it is called two-body abra- 
sive wear. If the particle is engaged 
by more than one other object, such as 
another wear surface or other abrasive 
particles, it is called three-body wear. 
Although the abrasive material is normal- 
ly harder than the wear object, this is 
not a necessary condition for classify- 
ing the wear as abrasive wear. Erosive 
wear is often categorized separately from 
abrasive wear. However, the erosive wear 
described in this report involves only 
solid particle erosion and therefore is 
considered as a type of abrasive wear. 

Dry-Sand, Rubber-Wheel 
Abrasive Wear Test 



Not included in this report are the 
frictional ignition tests at the Twin 
Cities, Albany, Avondale, and Pittsburgh 
(PA) Research Centers and the Los Angeles 
abrasion machine at Tuscaloosa Research 
Center. Although wear is inherent in the 
frictional ignition of methane-air mix- 
tures, the frictional ignition equipment 
is not used at present to study wear pro- 
cesses or wear mechanisms although it may 
be so used in the future. The Los Ange- 
les machine is for evaluating the abra- 
sion resistance of aggregates, such as 
those used for concrete or asphalt pav- 
ing. The tests, ASTM C131-81 and C565, 



The dry-sand, rubber-wheel (DSRW) abra- 
sion test apparatus simulates low-stress, 
three-body abrasive wear. This type of 
wear occurs in the mining industry in 
linkages, pivot pins, and wire ropes, 
which suffer slow wear from the sliding 
and rolling action of abrasive fragments 
of rock and ore trapped between metal 
surfaces. Because this type of wear is 
slow, field trials alone would be too 
slow for evaluating new materials. The 
DSRW abrasion test is quick and gives a 
reasonable correlation with field tests. 
Even before the test became an ASTM stan- 
dard (G65-81) in 1980 (5), it had been 



used by a number of laboratories for many 
years. Since becoming an ASTM standard, 
it has become probably the most popular 
abrasive wear test in the United States. 

The Society of Automotive Engineers 
(SAE) has developed but has not published 
a wet-sand abrasion test (8^) that is sim- 
ilar to the ASTM dry-sand test. Some ma- 
chines have been built to run both tests. 
SAE's wet-sand test has the advantage 
that the specimen does not heat as much 
as do the samples in a dry-sand test. 

DSRW Equipment and Specimen 

The basic ASTM machine consists of a 
rubber-rimmed steel wheel, 228.6 mm in 
diam by 12.7 mm wide, that turns at 200 
rpm during a test; a sand hopper con- 
nected by a tube to a nozzle that allows 
a 250- to 350-g/min sand flow; a revolu- 
tion counter that stops the drive motor 
after a set number of revolutions; and a 
weighted lever arm that holds the spec- 
imen and produces a horizontal force 
against the wheel where the sand is flow- 
ing. The sand is a 50- to 70-mesh silica 
test sand. The hardness of the rubber on 
the wheel must be durometer A-60±2. 

The Bureau's machine includes a strain 
gauge and a tachometer, as shown in fig- 
ure 1 , although they are not part of 
the ASTM standard. The strain gauge sup- 
ports the lever arm assembly at its pivot 
point, which is on a vertical line 
through the specimen-wheel interface. 
This allows measurement of the frictional 
force on the specimen during the wear 
test. The tachometer and a variable- 
speed drive make it possible to maintain 
a constant surface velocity on the rubber 
wheel as the diameter of the wheel de- 
creases through either wear or surface 
dressing. 

A typical test specimen is a rectan- 
gle, 25 by 76 mm, that is 3 to 13 mm 
thick. The wear surface is ground flat 
with a surface finish of at least 0.8 
urn. The density of the test material 
must be known, to calculate the vol- 
ume lost. The relatively simple shape 



-Sand hopper 



Sand nozzle 
Tachometer 




-Strain gauge 
■Pivot point 



Weight 



Specimen 
Rubber-lined wheel 




FIGURE 1. - Dry-sand, rubber-wheel abrasive 
wear test machine. 

of the test specimen is conducive to 
specimen preparation. Specimens of pure 
metals, steels, white cast irons, weld 
overlays, plastics, and ceramics have 
been made and tested. 

DSRW Procedure 

The equipment has two test parameters: 
the sliding distance (number of wheel 
revolutions) and the specimen load. The 
ASTM recognizes four procedures using 
these parameters, as shown in table 1. 

TABLE 1. - Standard conditions for the 
dry-sand, rubber-wheel abrasion test 



ASTM 
procedure 


Force on 
specimen, 

N 


Wheel 
revolu- 
tions ' 


Distance 

abraded, 

m 


A 


130 

130 

130 

45 


6,000 

2,000 

100 

6,000 


4,309 


B 


1,436 


c 


71.8 


D 


4,309 



^ Based on a diameter of 228.6 
Must be increased with wheel wear. 



A test consists of eight steps: 

(1) clean and weigh the specimen, 

(2) mount the specimen in the lever arm 
fixture and load the arm, (3) start the 
sand flow through the nozzle, (4) start 
the rubber-wheel drive motor, (5) release 
the lever arm so the specimen contacts 
the wheel and start the revolution coun- 
ter, (6) stop the motor (automatic) and 
sand flow, (7) remove the specimen, and 
(8) clean and reweigh the specimen. From 
the weight loss and density of the 
material, the volume loss is calculated. 
The test is repeated one or more times. 
The coefficient of variation on a mate- 
rial must not exceed 7 pet to meet 
ASTM specifications. 

DSRW Results and Discussion 

Most of the Bureau's testing has been 
with a 130-N load on the specimen and 
2,000 revolutions of the rubber wheel 
(ASTM procedure B) . Typical volume 
losses have ranged from 5 mm^ for sin- 
tered AI2O3 to 188 mm^ for pure iron, 
with losses for most steels ranging from 
30 to 120 mm^. The reproducibility of 
the test is best for volume losses in the 
range of 20 to 100 mm^. 

In tests in which less than 20 mm-' is 
lost, any small material inhomogeneities 
are exaggerated; therefore, a more severe 
test should be run by using either a 
greater sliding distance or more load. 
Above a 100-mm^ loss, the groove becomes 
so deep that it may contact the edge of 
the rubber wheel and cause erratic re- 
sults. Therefore, a less severe proce- 
dure may be desired. Using another pro- 
cedure has a disadvantage in that test 



results cannot be directly compared among 
different procedures. 

The DSRW test should be used only for 
ranking of various materials , not for ab- 
solute values of wear. For example, a 
material that wears half as much as 
another in the test probably will not 
last twice as long in the field because 
the test tends to exaggerate differences. 
Field factors such as the hardness and 
particle size of the abrading material 
will affect the absolute values of wear 
more than they affect the ranking. Typi- 
cal wear data are presented in table 2. 

Taber Abraser Test 

The Taber Abraser^ is a commercial wear 
tester designed to test the abrasive 
wear resistance of flat specimens of a 
wide variety of materials including coat- 
ings, paints, metals, plastics, paper, 
textiles, ceramic tile, and etched or 
printed material on glass. The wear con- 
dition can be classified as low-stress, 
two-body abrasive wear. The model 505 
Taber Abraser, located at the 
search Center, can test two 
simultaneously, a feature useful for rap- 
idly obtaining duplicate tests or for 
comparing two materials. 

Taber Abraser Equipment and Specimens 

Wear occurs by the action of a pair of 
abrasive wheels in contact with the spec- 
imen. The specimen is rotated at 72 rpa 

•^Reference to specific equipment is 
made for identification only and does not 
imply endorsement by the Bureau of Mines. 



Rolla Re- 
specimens 



TABLE 2. - Typical dry-sand, rubber-wheel abrasive wear data 



Alloy 


Hardness, 
HB 


Volume loss, mm-' 




Procedure A 


Procedure B 


Stainless steel, type 304.. 


156 


408 


160 


Mild steel, AISI 1020 


127 


ND 


133 


Low-alloy steel, ASTM A514. 


269 


ND 


122 


Austenitic 12Mn steel 


197 


ND 


57.1 


Low-alloy steel, AISI 5160. 


280 


ND 


51.3 


Cr white cast iron 


710 


31.5 


12.7 



Abrasive 




■Test specimen 

FIGURE 2. - Taber Abraser test, schematic. 



by a turntable, as shown in figure 2, 
which causes the abrasive wheels to drag 
and rotate. The horizontal axis of each 
abrading wheel is displaced from the ver- 
tical axis of the test material to pro- 
duce the abrading motion between wheels 
and specimen. The abrasive action re- 
sults in an "X" wear pattern over a 
ringed area of the specimen (fig. 3). 

Test specimens range from 10 cm square 
to 16 cm in diam, depending upon the 
specimen holder. A hole of 6.4 or 9.5 mm 
is required in the center of most speci- 
mens. An area of 30 cm^ is exposed to 
abrasion. The abrading wheels used for a 
test are selected to provide the desired 
abrasive quality. Five types of standard 
abrading wheels and other special wheels 
are available from the manufacturer. The 
wheels may contain silicon carbide or 
alumina abrasives over a range of parti- 
cle sizes and may be bonded with either 
rubber or resin. 

Taber Abraser Procedure 




FIGURE 3. - Wear pattern produced by the 
Taber Abraser. 



A test is conducted by placing the de- 
sired specimen on the turntable. The 
desired weight load is placed on the 
arms carrying the abrasive wheels. Loads 
of 125, 250, 500, or 1,000 g may be se- 
lected. The test is run continuously for 
a prescribed number of revolutions of the 
specimen: 10, 100, 1,000, or whatever 
the desired number. The count is dis- 
played, and the unit will automatically 
stop at the prescribed count. A vacuum 
pickup collects abraded particles. 

The test results may be evaluated 
by four methods , according to the 
manufacturer: 

1. Visual endpoint method. Certain 
materials are best evaluated by observing 
the point at which they undergo a marked 
change in appearance or break down physi- 
cally. By this method, the number of 
test cycles recorded on the counter is 
a wear index (rate of wear) of the sam- 
ple. Materials that lend themselves best 
to this method are plated, glazed, or 



polished surfaces; paper; textiles; and 
fabrics. 

2. Weight-loss method. The weight- 
loss method of evaluation can be used 
when test results are compared with those 
of similar materials with about the same 
density. In this case, the Taber wear 
index is the loss of weight in milligrams 
per thousand cycles of abrasion for a 
test performed under a specific set of 
conditions. 

3. Volume-loss method. When comparing 
the wear loss of materials of different 
density, it is usual to use the volume 
loss. The weight loss is converted to 
volxime loss by dividing by the density of 
the material. 

4. Depth-of-wear method. It may be 
desirable after abrasion tests to measure 
the depth of wear. This can be done with 
an optical micrometer calibrated in in- 
crements of one ten-thousandths of an 
inch. 

Because of the wide variety of materi- 
als tested, types of abrasive wheels, 
loads, and revolutions, typical results 
cannot be reported. For a mild steel us- 
ing a load of 1,000 g for 1,000 revolu- 
tions, the weight loss is about 30 to 60 
mg, depending upon the type of abrasive 
wheel used. 

Abrasion Resistance Test of 
Refractory Materials 

The Bureau's abrasion resistance test 
equipment for refractory materials is lo- 
cated at the Tuscaloosa Research Center. 
The equipment and test procedure are de- 
scribed in ASTM designation C704-76a, en- 
titled "Standard Method of Test for Abra- 
sion Resistance of Refractory Materials 
at Room Temperature" (6^) . The method 
covers the determination of the resist- 
ance of refractory brick to a sandblast 
stream. The test measures the volume of 
material abraded from a flat surface at 
a right angle to a nozzle through which 
1,000 g of size-graded silicon carbide 
grain is blasted by air at 448 kPa (65 



psi) . The test condition is classified 
as low-stress, two-body abrasive wear. 
The condition is considered low-stress 
because silicon carbide is tougher and 
more wear-resistant than the refractory 
brick normally tested. 

A schematic of the test equipment is 
shown in figure 4. A sandblast gun 
fitted with a glass nozzle directs the 
abrasive toward the brick test specimen, 
which is enclosed in a dust-tight cham- 
ber. A bag on the vent from the chamber 
collects the dust. The precision of the 
test was found by round-robin testing to 
be ±15 pet. 

Dry-Particle Erosive Wear Test 

Dry-particle erosive wear can be classi- 
fied as low-stress, two-body wear, the 
same type as in the preceding test. It 
simulates the wear conditions that occur 
in pipes , cyclones , and other equipment 
that carry fly ash or other particulate 
matter in a gas stream. A standard prac- 
tice for conducting a dry-particle ero- 
sive wear test has been developed by the 
ASTM G.2 committee on erosion and wear. 
This practice may be used in the labora- 
tory to measure the solid-particle ero- 
sion of different materials and has been 
used for ranking solid-particle erosion 
values of materials in simulated service 
environments (9-11). Actual erosion con- 
ditions involve particle sizes, veloci- 
ties , and environments that vary over a 
wide range (9^) in equipment such as cy- 
clones, dust collectors, etc. Although 
one laboratory test cannot simulate the 
many conditions under which erosion may 
take place, data obtained over a range of 
particle velocities and impingement an- 
gles can help in the selection of wear- 
resistant materials. 

Dry-Particle Equipment and Specimen 

The essential components of the appara- 
tus are shown in figure 5. The specimen 
is mounted in a chamber on a tiltable ta- 
ble to provide a range of Impingement an- 
gles . The specimen chamber is shown in 
figure 6. An abrasive material (normally 



50-ym, angular AI2O3) is carried by argon hose through a nozzle that consists of a 
(or some other gas) through flexible tub- tungsten carbide tube, 1.5 mm in ID by 
Ing. The gas-solid mixture exits the 50 mm long. The abrasive particles and 



Sand hopper 



A 



Media flow 
control system 



Sandblast gun 



Dust bag 



Manometer- 



\-/ 



^ 




ON- OFF 
valve 

Pressure 
/"regulator 

HL^ Air 



supply 



Door 



J-^ Nozzle 




\"^ Sample 




FIGURE 4. - Abrasion resistance test of refractory materials, schematic. 



/^^ 



Manometer 




3-way valve 
^AlgOs+Ar 



Thermometer 



Test chamber 



Abrasive 
trap 



Nozzle 
Specimen 



FIGURE 5. • Dry-particle erosive wear test 
apparatus, schematic. 

gas are mixed and fed by an S. S. White 
model H Airbrasive unit. Mixing is ac- 
complished within the Airbrasive unit by 
feeding particles from a pressurized con- 
tainer to a mixing chamber mounted on a 
vibrator. An orifice in the container 
bottom controls the flow of particles 
into the gas stream. The particle flux 
is a function of the voltage applied to 
the vibrator, and the velocity is a func- 
tion of the gas stream pressure. The 
particle velocity is calibrated by a ro- 
tating double-disk device described by 
Ruff and Ives ( 12 ) , and particle flux is 
calculated from the weight of abrasive 
collected in a given time. 



A novel feature of the Bureau's appa- 
ratus is its ability to collect the 
abrasive used during a test run. Other 
investigators' apparatuses rely on pre- 
weighing the abrasive or collecting the 
abrasive during a blank run. In the Bu- 
reau's apparatus, the abrasive passes 
from the specimen chamber to a filter 
where it is collected. A manometer and 
a thermometer are used to measure the 
pressure and temperature of the specimen 
chamber. 

Dry-Particle Procedure 

Particle velocity and flow are measured 
and adjusted to proper conditions be- 
fore specimens are tested. The specimens 
are polished through 400-grit abrasive, 
cleaned, and weighed to the nearest 0.1 
mg. After a specimen is mounted in the 
proper location and orientation in the 
apparatus, it is subjected to particle 
impingement for 10 mln. The specimen is 
then removed, cleaned, and reweighed, and 
the weight loss is calculated. The spec- 
imen volume loss is calculated by divid- 
ing the weight loss by the density of the 
specimen. The filter and specimen cham- 
ber are weighed before and after each run 
to determine the weight of abrasive used. 

Dry-Particle Typical Results 

Table 3 lists some typical test results 
for the erosive wear of 1020 steel, 304 
stainless steel, and white cast iron. 



TABLE 3. - Typical dry-particle erosive wear data: 
per gram abrasive 



erosion loss, 10 



-3 



Impingement 


Mild 


Stainless 


High Cr- 


Impingement 


Mild 


Stainless 


High Cr- 


angle. 


steel, 


steel, 


Mo white 


angle , 


steel. 


steel. 


Mo white 


deg 


AISI 
1020 


type 304 


cast iron 


deg 


AISI 
1020 


type 304 


cast iron 


30 m/s: 








70 m/s: 








15 


16.6 


15.1 


7.2 


15 


68.0 


62.3 


48.8 


30 


9.04 


12.3 


15.1 


90 


30.8 


31.8 


43.8 


45 


5.6 


10.9 


12.8 


103 m/s: 








60 


4.3 


9.1 


12.0 


15 


112.9 


101.9 


100.3 


75 


3.3 


7.8 


9.4 


90 


58.7 


55.1 


89.5 


90 


3.14 


4.66 


5.1 











NOTE. — 50-wm-diam AI2O3 particles carried by argon, 1.5-mm-diam nozzle. 



10 




FIGURE 6. = Dry-particle erosive wear test, specimen chamber. 



The data are expressed as the average 
volume loss of specimen per gram of abra- 
sive. The table shows the effect of par- 
ticle velocity and impingement angle on 
the wear of the specimens. At all three 
velocities, the high Cr-Mo white cast 
iron erodes less than the mild steel and 
stainless steel at a 15" impingement an- 
gle but erodes more than the mild steel 
and stainless steel at 90° impingement. 

Elevated-Temperature , Dry-Particle 
Erosive Wear Test 

Many industrial materials are subject 
to high-velocity abrasive particles at 
elevated temperature. Wear of this type 
is found, for example, in hot dust 



collection equipment. In order to select 
and develop materials for high-temper- 
ature use and to study the basic mecha- 
nisms of hot erosion, a laboratory test 
is necessary. Much has been learned 
about erosion at ambient temperature (10- 
13 ) , but elevated-temperature work has 
been very limited. An apparatus suitable 
for studying hot erosion was designed and 
constructed by the Bureau. The test con- 
ditions are similar to those of the 
dry-particle erosive wear test, just dis- 
cussed , except that the temperature can 
be elevated and the atmosphere can be 
controlled. 

Three elevated-temperature erosion test 
devices have been reported. Doyle and 



11 



Levy ( 14 ) described a device capable of 
testing specimens from room temperature 
to 1,000° C with particle velocities 
ranging from 30 to 180 m/s. The angle of 
impingement could be varied. The speci- 
men was heated in a small furnace, and 
the gas particle mixture was preheated. 
Young and Ruff (15) described a similar 
device, except the specimen was heated by 
passing an electrical current through it. 
Hansen ( 16 ) described the Bureau's appa- 
ratus in greater detail. 

Elevated- Temperature Erosive 
Equipment and Specimens 

The elevated-temperature erosion tester 
devised by the Bureau is shown sche- 
matically in figure 7. The apparatus 
consists of a vessel that contains a 
multiple-specimen holder on a turret, an 
electrical resistance heating element, a 
particle delivery nozzle, a shutter to 
conrol the abrasive blast duration, ther- 
mocouples , and an infrared pyrometer to 
monitor the temperature of the specimen 
surface within 10° C. The abrasive par- 
ticles, typically 27-ym AI2O3, are deliv- 
ered by an Airbrasive unit, as described 
in the preceding section. The particle 
delivery nozzle consists of a molybdenum 
shank about 4 cm long and a 1.3-cm sap- 
phire tip, 0.058 cm in ID. The multiple- 
specimen holder accommodates 12 speci- 
mens, any one of which can be positioned 
beneath the nozzle during a run. The an- 
gle of incidence of the particles strik- 
ing the specimen can be set by placing a 
wedge under the specimen. A vent in the 
vessel allows the driving gas to escape. 



Test specimens are approximately 1.5 
by 1.5 by 0.2 cm. The test surface is 
ground through 400-grit abrasive. 

Elevated-Temperature Erosive Procedure 

Specimens are cleaned, dried, and 
weighed before testing. After 12 speci- 
mens are placed on the turret, the test 
chamber is sealed, heated in a partial 
vacuum, and filled with the desired gas, 
typically nitrogen. About 30 min is 
required to attain a temperature of 
700° C. With the shutter closed between 
the nozzle and the specimen, the particle 
blast is started. After steady-state 
conditions are reached, the shutter is 
opened and the first sample is eroded 
for the desired time, typically 3 min. 
The remaining 11 specimens are eroded in 
the same manner. The furnace is then 
cooled by a stream of nitrogen gas and 
the specimens are removed, cleaned, and 
reweighed. 

Three standard specimens made of Haynes 
Stellite wrought alloy 6B are run with 
the nine test specimens in each test. 
The volume loss of each specimen is cal- 
culated from its weight loss and density. 
The data are reported as the ratio of 
volume loss to the average volume loss 
for the three Stellite standard speci- 
mens. This ratio is referred to as the 
relative erosion factor (REF) . 

Elevated-Temperature Erosive Results 

Table 4 contains erosion data for sev- 
eral materials tested at 700° C using 



TABLE 4. - Hot erosive wear of several materials 



Material 



Nominal composition, wt pet 



Relative erosion factor 



MgAl oxide 

Co-based hardf acing 

Do 

Stainless steel, type 304... 
Stainless steel, type 316... 

SiC, hot pressed 

B4C, hot pressed 

Si3N4, hot pressed 



97MgAl204-3MgO , 

Co-31Cr-12.5W-2.4C , 

Co-30Cr-4.5W-1.5Mo-1.2C 

Fe-17Cr-9Ni-2Mn-lSi 

Fe-17Cr-12Ni-2Mn-lSi-2.5Mo, 

NAp , 

NAp , 

NAp , 



2.76 
1.61 
1.00 
.73 
.56 
.44 
.21 
.12 



NAp Not applicable. 

NOTE. — 700° C, 90° impingement, 27-ym AI2O3 particles, 5-g/min particle flow, 170- 
m/s particle velocity, 3-min test duration, N2 atmosphere. 



12 



Turret drive 



Turret lock 



Pyrometer port 
Gas and abrasive inlet 




Insulation 



FIGURE 7. - Elevated-temperature erosion tester, schematic. 



nitrogen gas and 27-yni AI2O3 particles at 
90° impingement. The data reflect the 
average values for a set of five tests. 
One standard deviation of a set of tests 
was typically within 10 pet of the mean. 
The data reported include a wide range of 
REF values. 



Low-Angle Slurry Pot Test 

Transporting minerals as a slurry is 
an efficient means of transportation and 
is done during many mineral beneficia- 
tion processes. However, the movement of 
slurries can cause significant wear to 



13 



the slurry-handling equipment, especially 
in places where the flow changes direc- 
tion. Wear caused by slurries is an eco- 
nomic concern of industry. Pumps, el- 
bows, tee junctions, and hydrocyclones 
are component parts of slurry transport 
systems that are exposed to severe wear. 
In a slurry, abrasive erosion is produced 
by the solid particles, and corrosion may 
be produced by the liquid; the two are 
frequently synergistic. Reliable experi- 
mental wear data are needed to aid in the 
design of slurry transport equipment. 

Types of slurry wear tests reported in 
the literature include slurry pot, pipe- 
line, and jet impingement. All of these 
involve low-stress, two-body abrasive 
wear. Many variations of a slurry pot 
test have been devised. Jackson (17) 
used a rotating wire, Tsai ( 18) used two 
rotating metal tubes, and Bess ( 19 ) used 
a rotating disk as specimens in baffled 
pots containing abrasive slurries. These 
slurry pot tests relied on experimen- 
tal reproducibility because only one type 
of specimen was used in any one test. In 
addition, the impingment velocity was 
based on the assumption that baffles in 
the pot held the slurry stationary. 
Postlethwaite (20) , Hocke and Wilkinson 
(21), and Elkholy ( 22 ) used closed-loop 
slurry pipeline test systems. Postle- 
thwaite used rectangular specimens that 
were flush with the inside wall of the 
pipeline, and Hocke used rectangular 
specimens with a slurry jet impingement 
tester. All of the above-mentioned slur- 
ry wear tests have the problems of 
abrasive particle degradation and slurry 
contamination by wear debris. These 
problems are inherent in tests that re- 
circulate the slurry for prolonged times. 
The low-angle slurry pot test devised by 
the Bureau is normally operated in a 
flowthrough mode that essentially elimi- 
nates the problems of particle degrada- 
tion and slurry contamination. 

Slurry Pot Equipment and Specimens 

The Bureau's slurry test apparatus is a 
slurry pot consisting of an impeller that 
rotates the slurry past an array of 



specimens located around the inside of 
the pot. Thus, the impingement angle is 
low or nearly tangential. A schematic of 
the equipment is shown in figure 8. The 
slurry pot consists of a plastic ring 
with 16 sides that form a hexadecagon to 
hold specimens. This central section is 
bolted to a stainless steel top and bot- 
tom and is sealed with 0-rings. In order 
to avoid galvanic effects between unlike 
specimens , eight specimens are alternated 
with eight plastic inserts around the in- 
side of the plastic ring. Both the spec- 
imens and plastic inserts are 24 by 32 mm 
and 10 mm thick. The plastic inserts are 
made of ultrahigh-molecular-weight poly- 
ethelene, which has proven very wear re- 
sistant. The ends of the specimens are 
beveled to fit adjacently inside the 
plastic ring. The test surface of the 
specimen is surface-ground and polished 
through 400-grit abrasive before each 
test. 

The impeller is made from a commer- 
cial helical gear made of hardened steel 
that rotates to move the slurry past the 
stationary specimens. Dry sand is fed 
through a nozzle to a slurry hopper where 
the sand is mixed with the liquid. In 
tests conducted with this flowthrough 
system, typically, tapwater is fed to the 
system at a rate of 4.34 L/min and the 
sand is fed at 88 g/min, which results in 
a mean retention time for the sand in the 
slurry pot of only 2 s. The slurry dis- 
charges to a settling basin where the 
solids settle and the water flows to a 
drain. A modified drill press supports 
the slurry pot and drives the helical 
gear. A magnetic pickup provides a means 
to electronically measure the impeller 
tip speed, which can be varied from 1.3 
to 22.4 m/s by changing the belt system 
in the drill press. The temperature of 
the slurry is monitored at the discharge 
of the slurry pot. The equipment is il- 
lustrated in figure 9. 

Alternatively, the slurry can be recir- 
culated by shifting the slurry discharge 
back into the slurry hopper, as shown in 
figure 8. This alternate mode can be 
used to study the changes in particle 



14 



Liquid 
supply 



Slurry 
hopper 




Dry abrasive hopper 



Abrasive nozzle 



Liquid 
overflow 



^::) 



o 



Impeller 




^^^ y^>\ \,\ ^x\\\\\\\x\\\\\\^ 



Alternate circuit 
for recycled slurry 
test 



Slurry 



^m m^m 




flow 

Rectangular 
specimen 



Specimen 
holder 

Circuit for 
flow-through 
slurry test 



Pump 

FIGURE 8. - Low-angle slurry pot equipment, schematic. 



Slurry 
recovery 



15 




FIGURE 9. - Low-angle slurry pot test equipment. 



16 



shape and roughness and their effect on 
wear rates. Tests such as these also can 
be used to characterize wear mechanisms . 

Slurry Pot Procedure 

Specimens are prepared for testing by 
cleaning, drying, and weighing to the 
nearest 0.1 mg. Up to eight specimens 
along with the plastic inserts are placed 
inside the plastic center ring. Replace- 
able inserts above and below the speci- 
mens ensure that the specimens are elec- 
trically insulated from the stainless 
steel top and bottom sections. 

The mass flow rates of the dry abra- 
sive solids and the solution are each 
adjusted prior to the test to provide 
the desired percent solids and slurry 
flow rate. After the solution is pumped 
through the system for a few seconds , the 
helical gear and sand flow are started, 
and the time is noted. After a predeter- 
mined test time, the slurry pump and hel- 
ical gear are stopped, and the samples 
are removed, cleaned, dried, and weighed. 
The specimens are put back into the slur- 
ry pot, and the test is repeated sev- 
eral times. The volume losses are calcu- 
lated and recorded as a function of time. 
Curves of time versus volume loss are 
then compared with data obtained with 
standard AISI A514 steel specimens. The 
test procedure in the recirculating mode 
is essentially the same, except the per- 
cent solids is determined by the initial 
mass of solids and solution put into the 
system. 



One of the attributes of the flow- 
through system is that the temperature of 
the slurry is nearly constant and is de- 
termined by the temperature of the liquid 
supply. When recycled slurry is used, a 
means of heat exchange at the slurry hop- 
per is required to prevent overheating of 
the system. 

Specimens can be reused after regrind- 
ing and repolishing the wear surface and 
regrinding one beveled edge. Plastic 
inserts are placed behind the reground 
specimens in order to maintain the same 
clearance between the rotating gear and 
the specimen surface. This assures the 
same geometry inside the pot and gives a 
constant exposed area of wear surface. 
The size of the specimens allows two to 
be made from each previously worn speci- 
men from dry-sand, rubber-wheel abrasive 
wear tests or jaw crusher tests. 

Slurry Pot Results 

Typical results of wear testing with 
the low-angle slurry pot are presented in 
table 5 for both flowthrough and recy- 
cled slurry tests. Results of the flow- 
through tests showed that the wear rate 
is constant with respect to time. In 
contrast, conventional slurry tests that 
use a recycled slurry give decreasing 
wear rates with time (17-22) . In addi- 
tion, table 5 shows that lower wear rates 
were obtained with recycled silica sand. 
The lower wear rates result from the 
rounding of the slurry particles during 
the test. The ranking of specimens with 



TABLE 5. - Typical low-angle slurry wear data for several 
metallic specimens: wear rate, cubic millimeter per hour 



Specimen type 



Flowthrough 
slurry 



Recycled slurry 



0.33 h 



0.67 h 



1 h 



Stainless steel, type 304. 
Low-alloy steel, ASTM A514 
Mild steel plus 2 pet Si.. 
Low-alloy steel, AISI 4342 

Ni-based hardf acing 

Co-based hardfacing. ...... 



22.1 
21.1 
21.2 
6.99 
3.56 
2.40 



12.1 
6.10 
5.42 
1.60 
1.36 
1.46 



4.85 
2.54 
.274 
.028 
.778 
.163 



1.94 
1.06 
.014 
.001 
.444 
.018 



NOTE. — Water with 2-pct silica sand (minus 50 plus 70 mesh), 
17° C, 15.7 m/s. 



17 



respect to wear rate also can change dur- 
ing a recycled slurry test. For exam- 
ple, after 1 h, the fifth specimen had 
a greater wear rate than the fourth 
specimen. 

Jaw Crusher Gouging Abrasion Test 

Gouging wear occurs in many mining op- 
erations, for example, where excavator 
teeth or loaders penetrate or drag over 
rock, and in jaw and gyratory crushers. 
Gouging wear is identified by the removal 
of a significant amount of material (a 
gouge) from the wear object after an en- 
counter by the abrasive object in which 
the abrasive object also suffers damage. 
It is a type of high-stress wear that may 
be produced by either two-body or three- 
body conditions. The jaw crusher test 
gives high-stress, three-body abrasive 
wear. Jaw crusher wear tests were pio- 
neered in the United States by Borik (23- 
24) , improved by Fuller, ^ and used abroad 
by Sare and Hall (25). The jaws that 
crush the rock are taken as the test 
specimen. Several investigators believe 
that the jaw crusher test gives the 
closest correlation to wear that occurs 
on earth-penetrating equipment, such as 
excavator teeth, power shovel buckets, 
scoops, and grader blades, as well as 
real jaw crusher wear. ASTM committee 
G.2 has developed a new standard prac- 
tice for the jaw crusher gouging abrasion 
test. 

The Bureau's jaw crusher test equip- 
ment is considerably smaller than any re- 
ported in the literature. The smaller 
size gives greater economy of rock con- 
sumed and smaller specimen size. Typical 
values for the Bureau's test con^jared 
with typical values used in previous 
tests are — rock consumed, 91 kg versus 
910 kg; specimen size, 1 by 2.5 by 7 cm 
versus 2 by 7 by 15 cm; and specimen 
weighing precision, ±1 mg versus ±100 mg. 

^Fuller, W. (Esco Corp., Portland, OR). 
Private communication. 



Jaw Crusher Equipment and Specimen 

A small commercial laboratory jaw 
crusher was modified to accept an easily 
machined, identical pair of test wear 
plates and a similar pair of reference 
wear plates . One test plate and one ref- 
erence plate are attached to the station- 
ary jaw, and the other test and reference 
plates are attached to the movable jaw, 
such that a test plate and a reference 
plate oppose one another. A rock hopper 
and rock chute are attached above the 
jaw crusher. The arrangement of the jaw 
crusher test equipment is shown in fig- 
ure 10, and a photograph is presented in 
figure 11. The jaw crusher operates at 
260 c/min. 

The jaw crusher was extensively rebuilt 
and strengthened in order to transform it 
from a crude laboratory crusher into a 
precision wear test apparatus. The jaw 
opening, originally 7.5 cm (3 in) wide, 
was reduced to 5 cm (2 in) , thus pro- 
viding a specimen width of 2.5 cm (1 in). 
An alloy steel eccentric shaft of larger 
diameter was made, heattreated, and 
fitted with needle bearings. New bearing 
blocks were made and welded to reinforced 
side plates. New jaws that would hold 
test specimens were made, and the jaw 
opening adjuster was redesigned and re- 
built. The original 1.1-kW drive motor 
was replaced with a 3.7-kW motor. Be- 
cause of the many modifications, it is 
recommended that anyone wanting a jaw 
crusher test machine should design and 
construct a completely new unit instead 
of rebuilding an existing jaw crusher. 

The test wear plates and reference wear 
plates have a 15° taper on each end for 
clamping to the jaws. All specimen 
surfaces are machined on a surface 
grinder. The small size of the specimens 
has a distinct advantage because previ- 
ously used specimens from dry-sand, 
rubber-wheel abrasion tests can be used 
in the jaw crusher after regrinding. The 
standard reference material used is a 



18 



Sliding gate 

Movable jaw 
Fixed jaw 

Specimens 



Roller bearings on 
eccentric shaft 




Motor 



-Toggle 

FIGURE 10. - Jaw crusher gouging wear test machine, schematic. 



low-alloy steel, ASTM A514, 
ell hardness of HB 269. 



with a Brin- 



The test gives wear of a test material 
relative to a standard steel. Because 
the test is relative, variables in the 
rock have little effect on test results. 
Therefore, the size distribution and min- 
eral composition of the rock are not 
specified. 

Jaw Crusher Procedure 

After the four wear plates are cleaned 
and weighed to ±1 mg, they are clamped to 
the jaws with a standard plate opposing a 
test plate. The minimum jaw opening is 
set to 3.18 mm (0.125 in), and a 45-kg 
load of prescreened rock, minus 2 cm 
(3/4 in), is run through the crusher. 
The minimum opening is reset to 3.18 mm, 
and another 45 kg of rock is crushed. 
The specimens are recleaned by vigorous 
scrubbing with a bristle brush. The 
volume loss may be calculated from the 



mass loss, determined by weighing, and 
the known densities of the test materi- 
als. A wear ratio is developed by divid- 
ing the volume loss of the test plate by 
the volume loss of the reference plate. 
This is done separately for the station- 
ary and movable plates. The two wear ra- 
tios are then averaged for a final test 
ratio. The smaller the figure for the 
wear ratio, the better the wear resist- 
ance of the test plate. 

Jaw Crusher Typical Results 

After crushing 90 kg of rock, the typi- 
cal weight loss of the standard steel 
specimen was 0.4 g on the fixed jaw and 5 
g on the movable jaw. The wear ratios of 
test specimen to standard steel are given 
for several materials in table 6. Tests 
on materials having greater abrasive wear 
resistance than the standard gave wear 
ratios less than 1. For example, hard- 
ened AISI 4340 steel gave a wear ratio of 
0.157, and a high Cr-Mo white cast iron. 



19 




FIGURE n. • Jaw crusher gouging wear test machine. 



20 



TABLE 6. - Typical jaw crusher gouging wear data 



Alloy 


Hardness, 
HB 


Wear ratio 


Low-alloy steel, ASTMA514.... 
Austenitic 12Mii steel. ........ 


269 
187 
603 
588 
555 


1.000 ±0.030 
.284 


Low-alloy steel, AISI 4340 

6Ni-8Cr white cast iron 

High Cr-Mo white cast iron.... 


.157 
.134 
.0823 



NOTE. — Minimum jaw opening set at 3.18 mm (0.125 in); 
standard jaw of A514 steel, HB 269; 90 kg (200 lb) of 
rock crushed. 



known for its superior abrasive wear re- 
sistance, gave a wear ratio of 0.0823. 

The precision of the jaw crusher is de- 
termined after every six test runs. This 
is done by making a run in which all four 
specimens are of the standard steel. The 
average wear ratio of the two pairs of 
specimens must be 1.000±0.030, according 
to ASTM recommendations on the jaw crush- 
er test. The average ratio for the Bu- 
reau's tests fell within this limit. 

Ball Mill Wear Test 

When a lump of ore is crushed by the im- 
pact between two balls in a ball mill, 
it is considered high-stress, three-body 
abrasive wear. The abrasive wear of 
balls that results from the milling of 
ore is the major wear loss in most miner- 
als processing plants. During the wet 
milling of ores , abrasive wear is com- 
bined with corrosion. Abrasion and cor- 
rosion are synergistic: a corroded sur- 
face is more easily abraded than an 
abraded surface and an abraded surface is 
more easily corroded than a corroded pas- 
sivated surface. Thus, each enhances the 
other. Natarajan ( 26 ) showed that abra- 
sive wear loss was much greater than cor- 
rosion loss on steel balls during the 
laboratory ball milling of magnetic tac- 
onite. Bond ( 27 ) reported that wear 
rates during grinding became extreme as 
the pH of the liquid dropped below 5.5. 
Ellis ( 28 ) did extensive tests on the ef- 
fect of pH and atmosphere on steel balls 
while wet grinding sand in small 0.3- and 
1-m-diam mills. Norman and Loeb (29) 



extended the work to include the grinding 
of molybdenum ore in 3-m-diam mills. 

The Bureau set up an apparatus to study 
wear caused by erosion-corrosion of spe- 
cific ores and liquids. Two sizes of 
mills are used, a small mill, 12 cm ID, 
and a larger mill, 60 cm ID. The smaller 
mill is more convenient for laboratory 
research, but the surface of the test 
specimens may passivate because the small 
impacts may not significantly abrade the 
protective layer. That is, synergism may 
not occur. The larger mill assures more 
aggressive abrasion that is closer to the 
conditions in commercial mills. 

Ball Mill Equipment and Specimens 

The small ball mill is a commercial 12- 
cm-diam porcelain mill with five silicone 
rubber lifters added inside. The drive 
rotates the mill at 120 rpm. Figure 12 
shows the mill with typical specimens, 
rock, and liquid for a run. 

The larger ball mill (fig. 13) , is 60 
cm in diam by 20 cm long. It was fabri- 
cated from steel and lined with natural 
rubber, 1 cm thick. The interior of the 
mill has 12 lifters, each 2 cm high. In 
operation, the mill is entirely closed 
except for a vent in the center to pre- 
vent buildup of gas pressure. One end of 
the mill can be unbolted and removed for 
loading specimens, rock, and liquid. The 
mill is rotated by two rollers driven by 
a 2.7-kW motor that drives the mill at 
43 rpm or 75 pet of critical speed. A 
wooden cover fits over the mill and drive 



21 




FIGURE 12. - Small ball mill with specimens, 
liquid, and ;ocI<. 



Drum, 60-cm diam 



Thermostat 




FIGURE 13.- Ball mill test equipment, schematic. 

assembly. A heater and thermostat within 
maintain constant temperature during a 
run. 

The specimens used in the small ball 
mill are oblate spheroids about 2 cm in 
diam by 1 cm thick. Specimens of a wide 



range of alloys are conveniently prepared 
in an inert atmosphere box by arc-melting 
the starting materials on a copper hearth 
plate. The surface finish of such speci- 
mens is relatively smooth and requires 
little or no further grinding before 
testing. 

The test specimens used in the larger 
mill are cylinders , 5 cm in diam by 5 cm 
long, that are conveniently made by 
cutting commercial 5-cm rods into 5-cm 
lengths. Noncommercial alloys are made 
by casting in a sand mold. The cast 
specimens are sandblasted and rough 
ground. 

Ball Mill Procedure 

To conduct a test in either ball mill, 
specific amounts of liquid and ore or 
rock are selected to provide a slurry. 
The ratio of ore weight to total surface 
area of the specimens is kept the same in 
both mills for comparison of results. 
Typically, 1.13 L of liquid, 3.8 L of 
ore, and six specimens are used in the 
larger ball mill. Test specimens are 
cleaned, dried, and weighed. The ore is 
put into the mill and is warmed to the 
desired operating temperature, normally 
35° C. The test specimens and liquid are 
added to the ore, and the temperature and 
pH are measured. The mill is then sealed 
and run at constant temperature. After 1 
h of running time, the mill is opened, 
the temperature of the slurry is mea- 
sured, and the specimens are removed 
and cleaned with water and a soft nylon 
brush. A sample of the slurry is fil- 
tered, and the pH is measured. The tests 
on a given material are repeated until 
a consistent trend in weight loss is ob- 
tained. The surface area of each speci- 
men is determined, and from the density 
and mass loss during the test time, the 
erosion-corrosion rate in mils per year 
(1 mil = 0.001 in) is calculated. 

Ball Mill Results and Discussion 

A study of erosion-corrosion of grind- 
ing media during the grinding of Florida 
phosphate rock with recycled waste phos- 
phoric acid showed some characteristics 



22 



of the two ball mills. This slurry was 
quite acidic, ranging from an initial pH 
of 2 to a final pH of 3 after the 1-h 
test. Erosion-corrosion wear data on 
four alloys are given in table 7. Cor- 
rosion-resistant materials , the nickel- 
base alloy, Hastelloy C-276, and the 
stainless steel, type 316, had good wear 
resistance in the small ball mill where 
impacts were small. In the large ball 
mill, however, the wear rate increased 
about 10 times. Apparently the larger 
mill produced impacts sufficient to re- 
move the passivated film, thereby allow- 
ing an erosion-corrosion synergism. The 
data show that the large ball mill should 
give a more accurate correlation with in- 
dustrial wet-grinding mills. 

TABLE 7. - Ball mill erosion-corrosion 
of several materials , using phosphate 
rock and waste phosphoric acid, 
mils per year 



Alloy 


13-cm 


60-cm 




mill 


mill 


Ni-Cr white cast iron 


2,590 


1,930 


High-C steel, AISI 1090.... 


2,240 


1,420 


Stainless steel, type 316.. 


118 


1,090 


Ni alloy, Hastelloy C-276.. 


47 


559 



Pin-on-Drum Abrasive Wear Test 

The pin-on-drum abrasive wear test in- 
volves high-stress, two-body abrasive 
wear. One end of a cylindrical pin spec- 
imen is moved over an abrasive paper, 
abrading material from the specimen and 
crushing the fixed abrasive grains. The 
wear is believed to simulate wear that 
occurs during crushing and grinding of 
ore — processes in which the abrasive par- 
ticles are crushed, therefore called 
high-stress abrasive wear. 

Considerable pin-abrasive wear testing 
has been conducted on pin-on-disk equip- 
ment, beginning with Robin's machine in 
1910 (30). This machine wore a pin sam- 
ple along a single track on the surface 
of an abrasive cloth fixed to the flat 
surface of a disk. Khruschov made a ma- 
jor improvement by making the pin follow 
a spiral path, like a phonograph, to 



always encounter fresh abrasive. The 
work on this type of machine, reviewed by 
Moore (31), helped establish the effect 
of many parameters , such as abrasive 
material and size, specimen load, and 
speed, on two-body abrasion. Climax 
Molybdenum Co. developed a pin-on-table 
machine ( 32 ) with several improvements 
over the pin-on-disk machine. Using a 
converted milling machine, the moving ta- 
ble with abrasive attached provided a 
constant surface speed. The test speci- 
men was rotated to abrade the pin surface 
from all directions. Using the operating 
parameters from the Climax machine. Mut- 
ton (33-34) at Melbourne Research Labora- 
tories developed a pin-on-drum abrasion 
machine in which a slowly rotating drum 
was substituted for the moving table. 
The Bureau's machine is very similar to 
the Melbourne machine except for a few 
minor refinements. These latter three 
machines all can use the same type of 
abrasive, path length, load, speed of 
abrasive, and rotational speed of the 
specimen. 

Pin-on-Drum Equipment and Specimen 

The equipment consists of a head that 
rotates the test specimen while travers- 
ing the length of a cylindrial surface of 
a rotating drum covered with abrasive pa- 
per (figs. 14-15). The head has three 
functions. First, it loads the specimen. 
Second, it translates the specimen slowly 
along the drum so that only fresh abra- 
sive is encountered. Third, it rotates 
the test specimen to produce wear scars 
in all directions across the end of the 
specimen. The applied load is normally 
66.7 N. The 0.5-m-diam drum is covered 
with abrasive cloth, either AI2O3, SiC, 
or garnet of the desired size, usually 
120 to 150 mesh. The abrasive cloth is 
obtained in rolls, 61 cm wide, from a 
commercial source. During operation, the 
pin traverses 12.7 mm parallel to the 
axis of the drum while the drum makes 
one revolution. The wear path is 1.6 m 
per drum revolution. The drum rotates at 
1.7 rpm to give a surface speed of 2.7 
m/min. The pin specimen rotates at 17 
rpm. Through a system of gearing, a 



23 




FIGURE 14. = Pin-on»drum abrasive wear test machine, schematic. 



single motor drives the entire machine, 
which automatically stops after complet- 
ing a preset number of drum revolutions. 
A gear-dlsengaglng mechanism allows repo- 
sitioning of the specimen at intervals of 
6.35 mm along the drum. 

The test specimen consists of a pin 
6.35 mm in diam by 2 to 3 cm long. Spec- 
imens are normally prepared by machining 
in a lathe; hard or brittle metal speci- 
mens are cut out by electrodlscharge 
machining and then are finish ground 
in a lathe. Specimens over a wide range 
of hardness, including soft magnesium 
and hardened white cast iron, have been 
evaluated. 



Pln-on-Drum Procedure 

A new test specimen is worn in for ap- 
proximately four revolutions, or until 
its entire end displays wear scars, be- 
fore beginning the test runs. The test 
of a material requires two runs — one on 
the test specimen and one on a standard 
specimen. The number of drum revolutions 
is chosen to provide a reasonable amount 
of wear, that is, about a 40-mg loss. 
This requires about 6 revolutions (9.6-m 
path) for soft materials and 12 or more 
revolutions for hard materials. After 
the test specimen has been run, the stan- 
dard specimen is run for the same num- 
ber of drum revolutions with its track 



24 




where 



FIGURE 15. » Pinion-drum abrasive wear test machine. 

exactly between the tracks left by the 
test specimen. The standard material is 
a low-alloy steel, ASTM A514, with a 
hardness of HB 269. The standard speci- 
men wear is used to correct for small 
variations in the abrasiveness of the 
abrasive cloth from lot to lot and within 
a given lot. 



W is the corrected mass loss of 
the test specimen per meter 
of path length, 

W^ is the measured mass loss of 
the test specimen for x num- 
ber of revolutions , 



S^ is the 



measured mass loss of 
the standard specimen for the 
same x number of revolutions , 



and 



is the long-term average mass 
loss of the standard specimen 
per drum revolution. 



Specimens are cleaned ultrasonically in 
water with detergent, rinsed in water, 
rinsed in alcohol, and air-dried before 
each weighing. 

Test materials of approximately the 
same density, such as irons and steels, 
can be compared by weight loss. Materi- 
als of differing density should be com- 
pared by volume loss. Thus, the wear is 
reported as cubic millimeters (volume 
loss) per meter (path length) for a 66.7- 
N load on the given abrasive. 

Pin-on-Drum Results and Discussion 



The corrected mass loss of a test spec- 
imen for a given abrasive type under a 
given load is 



W = 



1.6S, 



This test apparatus has proven useful 
in ranking a wide range of materials 
under the conditions of two-body, high- 
stress wear. Table 8 shows typical re- 
sults for a variety of materials, using 



TABLE 8. - Typical pin-on-drum wear test data 



Alloy 1 


Hardness , 
HB 


Wear loss, mm^/m 




120-grit AI2O3 


150-grit garnet 


Pure iron 


61 
127 


1.70 
1.67 


1.86 


Mild steel, AISI 1020 


1.52 


Low-alloy steel, AISI 8620.. 


176 


1.28 


1.35 


Low-alloy steel, ASTMA514.. 


269 


1.225 


1.29 


Low-alloy steel, AISI 4142.. 


200 


1.035 


1.124 


Low-alloy steel, AISI 5160.. 


280 


1.009 


1.054 


High-C steel, AISI 52100.... 


322 


.793 


.790 


Cr white cast iron 


410 


.446 


.267 



'Steels were in hot-worked condition; cast iron was 
condition. 



in as-cast 



NOTE. — 66.7-N load, 6.4-mm-diam pin. 



25 



AI2O3 and garnet abrasive cloth. The 
garnet gives a greater spread in wear 
values. The results show that wear on 
pure iron can be reduced to about one- 
half by alloying to form steel and to 
about one-fourth by alloying to make 
white cast iron. 

The reproducibility of the test has 
been very good. In repeating a test im- 
mediately, the coefficient of variation 
has been less than 2 pet. Results on ma- 
terials retested after several months' 
time with a different lot of abrasive 
cloth differed by less than 5 pet from 
the earlier results. 

A set of 12 specimens was used to com- 
pare wear on the Bureau's machine with 
wear on the pin-on-table test of Climax 
Molybdenum Co. The results gave very 
nearly the same ranking of materials, but 
the wear on the Climax machine was con- 
sistently about 11 pet less for the same 
load, path length, and abrasive type. 

High-Speed Impact-Gouging Test 

A new and promising method for trans- 
porting raw materials from a mine is by 
pneumatic pipeline. This method uses a 
flow of air to transport solid particles 
of rock or ore through a pipeline. Lift- 
ing ore from underground to the surface 
pneumatically has great economic poten- 
tial but is limited by severe wear prob- 
lems. Pneumatic conveying is currently 
used for backfilling underground mines 
and trenches, removing tunnel muck, and 
transporting coal and ores within an un- 
derground mine. 

During pneumatic transport, severe wear 
at pipe bends is caused by collision of 
solid particles with the interior of the 
pipe. The particles may be as large as 6 
to 10 cm across, traveling at speeds up 
to '40 m/s. Elbows have been known to 
wear through after only a few hours of 
use. A limited amount of research has 
been done to evaluate the erosive wear of 
bends used in pneumatic transport. Mills 
and Mason (35-38) used a closed-loop ex- 
perimental apparatus to simultaneously 



determine the wear rates of six pipe 
bends. Kostka ( 39 ) used coarse solid 
particles in a commercial-sized pneumatic 
transport system to study erosive wear in 
different types of pipe bends. 

No prior experimental apparatus has 
been developed to study the effect of 
high-impact abrasive wear caused by large 
particles with a mass greater than a few 
grams . The Bureau has designed and con- 
structed test equipment capable of shoot- 
ing a 1-kg projectile at a test specimen 
at speeds up to 45 m/s. The test has 
been named the high-speed impact-gouging 
test. The wear condition is classified 
as high-stress, two-body abrasive wear. 
The condition is considered high-stress 
because the abrasive projectile suffers 
appreciable damage during impact. 

High-Speed Impact Equipment 
and Specimen 

The test equipment consists of an air 
gun that shoots rock projectiles at a 
stationary specimen located a short dis- 
tance from the muzzle. The specimen 
stage can be tilted to vary the angle be- 
tween the projectile line of flight and 
the specimen surface. The test equipment 
is shown in figures 16 and 17. The pro- 
jectile is a cylinder 7 cm in diam by 10 
cm long, weighing 1 kg. Solid granite 
cores can be used, but for economy, a 
concrete cylinder with a granite disk 
about 2 cm thick on the impact end is 
used. A pin through the side of the tube 
holds the projectile in place while driv- 
ing gas is admitted to give the desired 
pressure. A chronograph is used to de- 
termine the velocity of the projectile 
after it exits the tube. A box below 
the impact area collects debris from the 
shattered projectiles, and a safety 
shield covers the end of the tube and the 
impact area. 

The test specimens are normally 7.6 
by 2.5 by 1.3 cm, with beveled ends for 
clamping. They are interchangeable with 
the jaw crusher test specimens previously 
described. 



26 



o 



Gas-pressure 
controls 



Oscilloscope timer 




FIGURE 16. - High-speed impact-gouging test machine, schematic. 



High-Speed Impact Procedure 

The specimens are cleaned, dried, and 
mounted on the target face, with the an- 
gle of incidence set by adjusting and 
locking the target. The tube is cleaned 
and sprayed with a Teflon fluorocarbon 
polymer coating that lowers friction and 
wear. The projectile is loaded into the 
tube, a rubber seal is placed behind the 
projectile, and the breech is closed. 
Gas is admitted to the chamber to a spe- 
cified pressure, the chronograph is set, 
and the projectile is released by actuat- 
ing the solenoid that retracts the re- 
taining pin. 

After the projectile is shot, the time 
recorded by the oscilloscope is noted and 
used to calculate the projectile veloc- 
ity. The target specimen is removed, 
cleaned with a brush, and soaked in con- 
centrated hydrofluoric acid in order to 
remove the embedded silicate material. 



The specimen is then dried and weighed. 
The barrel is cleaned for the next run. 

Although the test equipment is rela- 
tively new, several general findings can 
be reported. Examination of the specimen 
surfaces of mild steel after impact has 
revealed gouges resulting from ductile 
deformation. The gouge scars are much 
deeper but shorter at a 45° angle of im- 
pact than at a 15° angle. The harder 
steel alloy specimens have exhibited much 
smaller wear scars and indicate some de- 
gree of brittle fracture. It is possible 
that brittleness is induced by the high 
strain rate produced by this test. 

IMPACT-SPALLING WEAR 

Many types of ore crushing and grind- 
ing equipment, such as hammer mills, rod 
mills, and ball mills, subject wear parts 
to repetitive impacts. The wear that re- 
sults from fatigue, spalling, chipping, 



27 




FIGURE 17. - High-speed impact-gouging test machine. 



and fracturing can be more severe than 
abrasive wear. This is especially true 
of very hard alloys such as martensitic 
steels and alloyed white cast irons with 
their superior abrasion resistance but 
with a propensity to spall or break after 
large numbers of impacts (40) . Neither 
fracture toughness nor Charpy impact 
tests have proven useful for predicting 
behavior of the relatively brittle, wear- 
resistant materials subjected to repeated 
impacts (41). 



onto a test block, as described fully 
by Blickensderf er and Forkner ( 42 ) . The 
impacts are concentrated onto one rela- 
tively small area on the test block. 
Testing machines of similar concept were 
used previously by Dixon ( 43 ) and Durman 
(44). Machines of this type have been 
useful for obtaining laboratory data on 
the spalling and fracture resistance of 
materials subjected to repeated impacts. 

Ball-on-Block Equipment and Specimen 



Ball-on-Block Impact-Spalling Test 

A test that simulates the type of wear 
caused by repetitive impacts is the ball- 
on-block impact-spalling test. The test- 
ing machine drops steel balls repeatedly 



The machine consists of a steel frame, 
a conveyor for lifting balls, ramps for 
transporting balls , and an anvil for sup- 
porting a specimen inside a large fun- 
nel that collects the rebounding balls , 
as shown in figures 18 and 19. The 



28 



Conveyor drive motor 



Conveyor 



Buckets (45 cm 
apart) 



Guard screen 




8.3-cm-ID by 9-cm-OD 
steel pipe 



Frame 



Sand reservoir 



75-mm-diam balls 
3-m drop 



Guard screen 



Clamp 

Specimen (opprox 
5 by 15 by 20 cm) 

Anvil 



Rubber-lined hopper 
Hopper support stand 

Perforated chute 
Floor 



///////////// 



ffTfTTjy / 7 / /' //>/y/// 



FIGURE 18. - Bail-on-block impact-spoiling test machine, schematic. 



29 




FIGURE 19. - Ball-on-block impact-spa I ling test machine. 



30 



commercial steel balls used are 75 mm in 
diam and weigh about 1.8 kg. From the 
top of the conveyor, the balls roll into 
a vertical tube that directs them onto 
the test block after a fall of 3 m. Sil- 
ica sand is continuously fed onto the 
test block in order to more closely simu- 
late the condition in a ball mill wherein 
ore is present on the liners. The number 
of impacts is displayed by a counter that 
is actuated when a ball interrupts a 
light beam across the lower ramp. 

Test blocks are approximately 50 mm 
thick, 15 cm wide, and 20 cm long. The 
15- by 20-cm face is the impact surface. 
Blocks are surface-ground on the bottom 
to ensure good contact with the anvil. 
If the quality of a cast block is ques- 
tionable, it should be X-rayed first, in 
order that valuable test time is not 
spent on inferior materials. 

Ball-on-Block Procedure 

The test block is clamped securely 
to the anvil, and safety guards are in- 
stalled. The balls, normally 12, are 
placed in the machine. The sand flow and 
conveyors are turned on. With the con- 
veyor running at a speed of 38 m/min, 
about 2,000 impacts per hour are deliv- 
ered to the test block. A block is 
tested until it breaks or 100,000 impacts 
are delivered. During the test, the 
weight loss and size of the developing 
crater are measured at intervals of 
10,000, 20,000, 35,000, 60,000, and 



100,000 impacts. During operation, an 
area within 2 m of the machine is blocked 
off to prevent injury to personnel be- 
cause occasionally a ball escapes from 
the machine with sufficient energy to 
cause severe injury. 

Ball-on-Block Results and Discussion 

Four types of failures have been 
observed, namely, cold flow, flaking, 
spalling, and breakage. The softer and 
more ductile steel alloys tend to cold 
flow and flake. Cold flow describes the 
movement of bulk metal by plastic defor- 
mation and is identified by an impact 
crater and rounded edges of the block. 
Flaking describes the formation and sub- 
sequent separation from the surface of 
thin flakes of metal that develop from 
fatigue. Cold flow and flaking occur to- 
gether but to differing degrees depending 
upon the particular alloy. 

Spalling and breakage tend to occur on 
the harder (more wear-resistant) alloys. 
Spalling describes the separation of 
pieces of material of about 3- to 6-mm 
dimensions. A crater develops in the im- 
pact region as a consequence of spalling. 
If a block fractures into two or more 
major pieces, it is termed breakage. 
Blocks may or may not spall before break- 
age occurs , depending upon the composi- 
tion and heat treatment. 



Data showing typical test 
given in table 9. 



results are 



TABLE 9. - Typical ball-on-block impact-spalling data 





High-Cr-Mo 


Mild steel. 


Martensitic 


Ni white 




white 


AISI 1020 


Cr-Mo steel 


cast iron 




cast iron 








Hardness HB. . 


670 


156 


550 


580 


Number of impacts 


100,000 


100,000 


100,000 


14,000 


Type of failure 


Spalling 


0) 


Flaking 


Breakage 


Wt loss. . . .mg/impact. . 


5.1 


0.82 


0.09 


Neg. 


Crater size: 










Diameter cm. . 


10.7 


12.7 


5.8 


Neg. 


Depth cm. . 


1.1 


0.25 


0.28 


Neg. 


Volume cm^ . . 


21.7 


6.3 


1.1 


Neg. 



Neg. Negligible. 'Cold flow, flaking. 

NOTE. — 1.8-kg steel balls, 3-m drop height, 5-cm-thick test block. 



31 



Ball-on-Ball Impact-Spalllng Test 

The ball-on-ball impact-spalling test 
is designed to create large numbers of 
impacts on test materials in a relatively 
short time. Designed and constructed by 
the Bureau, the test is an advance over 
the earlier ball-on-block drop tests be- 
cause of at least a twenty-fold increase 
in testing speed. The test, described 
in greater detail by Blickensderfer and 
Tylczak ( 45 ) , has proven especially 
useful for studying the spalling of al- 
loyed white cast irons and for comparing 
the resistance to breakage of commercial 
and experimental grinding balls. Because 
the impacts are distributed randomly over 
the entire surface of the ball speci- 
men, the entire surface becomes highly 
stressed under compression. 

Ball-on-Ball Equipment and Specimens 

Balls are impacted against each other 
in a manner that provides many impacts 
in a relatively short time. A ball is 
dropped 3.5 m onto a column of balls con- 
tained in a curved tube, as shown in fig- 
ure 20. The impact from the dropped ball 
is transmitted through the column of 
balls with each successive ball receiving 
a ball-on-ball impact on each side. The 
kinetic energy of the first impact is 
54 J. The energy of subsequent impacts 
through the tube decreases until it is 
about 5 J at the last impact. The energy 
in the last ball carries it out of the 
end of the tube onto a ramp where the 
ball actuates a counter and rolls into a 
bucket conveyor that carries it to the 
top of the machine to be dropped again. 
The machine provides random occasional 
mixing of the balls as described in ref- 
erence 45, to give different neighbors to 
each ball over a period of time. 

Two advantages of the design are (1) it 
produces many Impacts quickly on a group 
of balls, and (2) the impacts are of var- 
iable intensity, as found in a real ball 
mill. 

The test balls are 75 mm in diam and 
weigh about 1.8 kg. Both cast and forged 
steel balls and cast iron balls have been 




FIGURE 20. - Ball-on-ball impact-spalling 
test machine, schematic. 



32 



used. Because many different ball speci- 
mens are run simultaneously, they are 
identified by grinding small flats on 
their surfaces. 

Ball-on-Ball Procedure 

To start a test, 22 balls are loaded 
into the machine. During operation there 
are typically 18 balls in the tube and 4 
in the ramps and in the conveyor buckets. 
The machine drops about 22 balls per min- 
ute. For each ball dropped, 36 impacts 
are created — two on each ball in the tube 
except the one dropped and the one leav- 
ing the tube. This gives a rate of about 
45,000 total impacts per hour in the sys- 
tem. The machine is run unattended. 
When a ball breaks , the pieces block the 
tube or ramp and all balls cease to cir- 
culate. Although the conveyor continues 
running, the ball drop count remains 
fixed on the counter. An area within 2 m 
of the machine is blocked off during op- 
eration to prevent injury to personnel 
because if a ball escaped from the ma- 
chine, it could cause severe injury to a 
person. 

Balls are tested until they break or 
until they spall excessively. Experience 
showed that balls that have spalled over 
150 g do not roll down the ramps; there- 
fore, a ball is removed from the test 
after it has lost 100 g by spalling. 
All balls are removed from the tube and 
weighed at intervals of 5,000 to 20,000 



impacts per ball. Accurate accounting of 
the impacts is kept on each ball. A ball 
that fails is replaced with either anoth- 
er test ball or a hardened steel filler 
ball, and the test is continued. 

Ball-on-Ball Results and Discussion 

Four types of failures have been ob- 
served: (1) spalling, pieces of 2 to 5 
cm across and up to 1 cm thick, (2) mini- 
spalling, small deep crescent pits 2 to 4 
mm across and 2 to 3 mm deep, (3) flak- 
ing, very thin flakes with extreme 
surface cold work, and (4) breakage, a 
complete failure of the ball, often by 
fracturing through the center of the 
ball. 

The type of failure of a ball seems to 
be dependent on hardness and the means by 
which the balls were produced. Spalling 
occurs mainly in cast balls and starts 
within 50,000 impacts. Minispalling oc- 
curs in forged, hard (about HRC 62 to 
64) steel balls and does not start until 
100,000 or more impacts. Flaking and 
plastic deformation are the only damage 
that occur to the softer (less than 
HRC 40) forged steel balls. The flakes 
develop after 60,000 or more impacts. 
Breakage occurs in fully hard (greater 
than HRC 63) steel balls and unheat- 
treated cast balls and can occur any time 
from a few to a few hundred thousand im- 
pacts. Additional results are presented 
by Blickensderfer (45-46). 



SUMMARY 



The research laboratories of the Bureau 
of Mines have the capability to conduct a 
large variety of wear tests relevant to 
the mining and minerals processing indus- 
tries. The tests include several perti- 
nent ASTM standard tests and proposed 
standard tests. The abrasive wear tests 
include one low-stress, three-body wear 
test (dry-sand, rubber-wheel abrasive 
wear test); five low-stress, two-body 
wear tests; two high-stress, three-body 
wear tests (jaw crusher and ball mill); 
and two high-stress, two-body wear tests 



(pin-on-drum and 
gouging) . 



high-speed impact- 



The repetitive impact tests include a 
ball-on-block impact-spalling test and 
a novel ball-on-ball impact spalling 
test. The latter is capable of producing 
impacts at a much faster rate than previ- 
ous tests of this type. 

Comparisons of the tests , test condi- 
tions , and other parameters are summar- 
ized in tables 10 and 11. 



33 





10 


































<u 








• 


" 




















bO 








CO 


01 




>, 






4H 


1 






n) 




<u 


C) 


(U 


<u 




M 






IH 


E 






>! 




01 


01 


u 


e 




o 






o 


•H 


u 




^ • 


a 


3 


3 


3 


t4 




4H 




rH 


o. 




01 




•H O 


CO 


O 


o 


4J 


rH 




CO 




rH 


01 


X 


4= 




rH a. 


• M 


J5 


J= 


CO 


CU 




M 




•H 


3 





44 




O 


01 0) 


60 


bO 


u 


O. 




>. 




P 


CO 


4- 


o 




- u 


r-l (3 


CO 


CO 


cu 


•rl 




60 




•3 


u 


Ct 




10 


03 


(U -H 


.o 


^ 


& 


a. 












4J 





* 


C 


c o 


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a 






•O 




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o 


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J2 


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rH 


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s >% 


0) 


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cc 






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p 


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g. 










0) 


44 




1 


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111 


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13 






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9 


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1) 


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c 


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a 


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0) 





• -ri 


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c 


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n) 


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3 




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60 








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to 


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CO 


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1 


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to 

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PC 


pa 





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m 


in r- 




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r~ O rH o CM 


rH O O 








O 

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m 




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P. 3 


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1 1 


1 


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m 




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CO -3 




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3 






P 


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3 




3 


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rH rH CM 1 O 




o 




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o o o 




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rH m rH 


MH 01 














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01 


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CM f-H a 


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r- 


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CO 


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XI 


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43 43 -3 




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m CM 


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60 








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to •H 




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44 








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1 




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01 


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tt 


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1 4J 


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01 


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3 


44 4J 


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01 1 1 


a 


3 < 


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0) « 


60 3 -H •H 1 

u c p a a 3 


(3< 3 3 


CO 


to 


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to CO 


44 C 


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z 


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01 


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1 


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p p 


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c 


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n 


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pa « 


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X 


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C 


CJ 


tH 


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a 


44 




3 


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01 


p 


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to 


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44 


01 


01 


01 




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3 



rH a 
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D. 44 



O 
Q. 3 

ZlM 



34 



REFERENCES 



1. American Society for Testing and 
Materials. Evaluation of Wear Testing 
(Sjrmp., 71st Annu. Meeting ASTM, San 
Francisco, CA, June 23-28, 1968). ASTM, 
Philadelphia, PA, Spec. Tech. Publ. 446, 
1969, 132 pp. 

2. Bayer, R. G. (ed.). Selection and 
Use of Wear Tests for Metals (Symp., 
Nov. Committee Week, ASTM, New Orleans, 
LA, Nov. 17-21, 1975). ASTM, Philadel- 
phia, PA, Spec. Tech. Publ. 615, 1975, 
111 pp. 

3. Borik, F. Using Tests To Define 
the Influence of Metallurgical Variables 
on Abrasion. Met. Eng. Q. , v. 12, No. 2, 
1972, pp. 33-39. 

4. Tweeton, D. R. Effect of Environ- 
ment on Friction and Wear Between Quartz 
and Steel. BuMines RI 8124, 1976, 25 pp. 

5. American Society for Testing and 
Materials. Standard Practice for Con- 
ducting Dry Sand/Rubber Wheel Abrasion 
Tests. G65-81 in 1981 Annual Book of 
ASTM Standards: Part 10, Metals — Phys- 
ical, Mechanical, Corrosion Testing. 
Philadelphia, PA, 1981, pp. 1044-1061. 



6. 



Standard Method of Test for 



Abrasion Resistance of Refractory Materi- 
als at Room Temperature. C704-76a in 
1981 Annual Book of ASTM Standards: Part 
17, Refractories, Glass, and Other 
Ceramic Materials; Manufactured Carbon 
and Graphite Products. Philadelphia, PA, 
1981, pp. 710-714. 

7. Bhat, M. S., V. F. Zackay, E. R. 
Parker, and I. Finnie. Wear Resistant 
Alloys for Coal Handling Equipment. 
Prog. Rep. for the period Oct. 1, 1977- 
Sept. 30, 1979, Rep. ZP8006. Univ. CA, 
Berkeley, CA, 1979, 63 pp. 

8. Borik, F. Rubber Wheel Abrasion 
Test. Pres. at SAE Combined National 
Farm, Construction & Industrial Machinery 
and Powerplant Meetings, Milwaukee, WI, 
Sept 14-17, 1970. SAE preprint 700 687, 
1970, pp. 1-12. 



9. Levy, A. V. The Solid Particle 
Erosion Behavior of Steel as a Function 
of Microstructure. Wear, v. 68, No. 3, 
1981, pp. 269-287. 

10. Head, W. J., and M. E. Harr. The 
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aU.S. CPO: 1985-505-019/5091 



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